And Malik related to me that he had heard that a man came toAbdullah ibn Umar and said, "Abu Abd ar-Rahman, I gave a man a loanand stipulated that he give me better than what I lent him." Abdullahibn Umar said, "That is usury." Abdullah said, "Loans are of threetypes:
A free loan which you lend by which you desire the pleasure ofAllah, and so you have the pleasure of Allah. A free loan which youlend by which you desire the pleasure of your companion, so you havethe pleasure of your companion, and a free loan which you lend bywhich you take what is impure by what is pure, and that is usury." Hesaid, "What do you order me to do, Abu Abd ar-Rahman?" He said, "Ithink that you should tear up the agreement. If he gives you the likeof what you lent him, accept it. If he gives you less than what youlent him, take it and you will be rewarded. If he gives you betterthan what you lent him, of his own good will, that is his gratitude toyou and you have the wage of the period you gave him the loan."
USC-MSA web (English) reference: Book 31, Hadith 93
Arabic reference: Book 31, Hadith 1379